Many utilities bury their pipes and/or cables (hereinafter, "conveyances") underground for cosmetic reasons. Such underground burial also helps protect utility conveyances from natural elements, such as wind, rain and sunlight. However, underground burial of utility conveyances renders them susceptible to other types of harm, such as accidental severing or breakage due to inadvertent excavation by a contractor. To prevent this type of harm, utilities record the location of each buried conveyance. Upon notification by a contractor of an intent to excavate, a utility determines whether it has any conveyance likely to be affected. If the utility has such an underground conveyance, the utility will dispatch a technician to mark its location.
In the past, utilities have used electromagnetic signaling to locate underground conveyances. To that end, the utility applies an alternating current signal at a unique frequency to each buried conveyance, either directly, or to a separate wire buried adjacent to the conveyance. A technician seeking to locate the conveyance employs a cable-locating detector (i.e., a Radio Frequency (RF) receiver) tuned to the frequency of the signal impressed on the conveyance. Because of stray electromagnetic signals radiated by other underground conveyances lying nearby, the technician may not be able to locate the exact position of the conveyance of interest. Thus, the technician may have to physically uncover the buried conveyance to establish its exact location. Given that many conveyances buried by the same utility have a similar appearance, the technician may locate and protect the wrong conveyance.
U.S. Pat. No. 5,438,265, issued on Aug. 1, 1995, and assigned to AT&T Corp., discloses a cable-locating device that overcomes some of the difficulties of the prior art devices. The locating device disclosed in the patent utilizes an RF detector and a viewing mechanism, such as a television camera, or the like, in combination, to precisely locate a buried utility conveyance. Although this approach affords a higher degree of precision, excavation means must be provided within the device for removing the earth in the vicinity of the cable to allow observation by the viewing mechanism. The need for such excavation means renders the cable-locating device of U.S. Pat. No. 5,438,265 somewhat complex and relatively expensive.
Thus, there is a need for a simplified, lower-cost technique for locating a buried utility conveyance.